Subject: Abstract: Natural Markings
The following paper has recently been published which may be of interest to
Peter T. Stevick, Per J. Palsbøll, Tim D. Smith, Mark V. Bravington and
Philip S. Hammond. 2001 Errors in identification using natural markings:
rates, sources and effects on capture-recapture estimates of abundance.
Canadian Journal of Fisheries and Aquatic Sciences 58:1861-1870.
The results of a double-marking experiment using natural markings and
microsatellite genetic markers to identify humpback whales (Megaptera
novaeangliae) confirm that natural markings are a reliable means of
identifying individuals on a large scale. Of 1410 instances of double tagging
there were 414 re-sightings. No false positive and 14 false negative errors
were identified.The rate of error increased with decreasing photographic
quality; no errors were observed among photographs of the highest quality
rating while an error rate of 0.125 was identified in sightings for which
only part of the area used for identification was visible. There was also a
weaker relationship between error rate and the distinctiveness of markings,
which may result from non-independence in coding for image quality and
distinctiveness. A correction is developed for the Petersen two-sample
abundance estimator to account for false negative errors in identification
and a parametric bootstrap procedure for estimation of variance is also
developed. In application to abundance estimates from the North Atlantic, the
correction reduces the bias in estimates made using poorer quality
photographs to a negligible level while maintaining comparable precision.
A limited number of reprints are available. Please contact Peter Stevick, PO
Box 93, Rockport, ME 04856, USA <PeterStevick@aol.com>.
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